(i) Technical Field
The present invention relates to an electrostatic charge image development carrier, an electrostatic charge image developer, a process cartridge, an image forming apparatus, and an image forming method.
(ii) Related Art
Electrophotography that visualizes image information using an electrostatic charge image is currently utilized in various fields. In electrophotography, a method has been normally used in which an electrostatic charge image is formed on a latent image supporting body (photoconductor) or an electrostatic recording body using various units, and then developed/visualized by attaching charge-detecting particles called toner to the electrostatic charge image. A developer used herein is broadly classified as a two-component developer in which an appropriate amount of positive or negative charge is provided to toner by causing triboelectrification between particles called a carrier and toner particles, or a single-component developer that uses toner alone, such as magnetic toner. In particular, a two-component developer is widely used because the functions, such as stirring, conveying, and charging, required for a developer are separately provided to a carrier itself and thus the developer is easily designed.
In recent years, higher image quality, higher-speed processing, and long term stability of images formed with an image forming apparatus that uses electrophotography have been required. To satisfy such higher image quality, it has been increasingly considered that the size of toner particles be reduced and the charge amount of toner be made uniform and stabilized. With the reduction in toner particle size, it has also been considered that the size of carrier particles be reduced and the particle size distribution be narrowed. To achieve a uniform and stable charge amount, a core composition, a coating resin composition, and the like have been considered, which results in achieving even greater functionality.
A carrier needs to have a characteristic of charging toner in a desired charge amount as uniformly as possible. To achieve such a characteristic, a carrier and toner need to be uniformly mixed with each other and the surface characteristics of the carrier need to be more uniform. If the mixing is insufficient or the surface of the carrier is nonuniform, the charge amount easily becomes nonuniform. Furthermore, to adjust the charge amount of toner to a desired value or to stabilize the charge amount of toner used for a long time, the electrical resistance of the carrier needs to be adjusted. This is achieved by a publicly known method in which the surface of a carrier is coated with a resin, and conductive powder such as carbon black is dispersed in the resin layer to adjust the electrical resistance.